EP-A-410500 discloses an imaging element containing a support provided with an image receiving layer and a silver halide emulsion. In said document is disclosed a diffusion transfer reversal process (hereinafter called "DTR process") for obtaining a lithographic printing plate in which said imaging element (further commonly indicated as "printing plate") is imagewise exposed and subsequently developed using a developing liquid or activating liquid in the presence of a silver halide complexing agent. The printing plate is then guided through a diffusion transfer zone so that the silver halide complexes formed during the development step are allowed to diffuse into the image receiving layer where they are converted to silver. When the printing plate leaves the diffusion transfer zone a silver image is formed in the image receiving layer. Hereafter, the printing plate passes a washing and a rinsing station to remove the silver halide emulsion layer so that the silver image is exposed. Finally the printing plate, now carrying a silver image-on its surface, is treated with a finishing liquid that contains a so called hydrophobizing agent for improving the hydrophobicity of the silver image.
In an apparatus or system for the developing of such lithographic printing plates it is advantageous to maintain the length of the developing path of the printing plate in the processing liquids within specified limits so as to achieve high quality printing plates.
By controlling the length of the developing zone and the transportation speed of the printing plate, the time of development can be controlled. However, experience shows that, even if the developing time is under control, some density differences on the printing plate still may be present. Even if in addition of the developing time, also the developing fluid is under control regarding fluidlevel and flowrate and flowdistribution within the developing bath, as well as other physical and chemical characteristics (as e.g. temperature and photographic activity) a prohibitive uneveness in density remains perceptable.
At this point, a particular problem exists in the accurate geometrical control of the whole developing path of the plate, clearly including the entrance of the plate in the bath and also the exit from the bath, because some disturbing transients may occur at those positions, as e.g. first a temporary "swimming" of the printing plate on the developing fluid (caused by surface tension) and a sudden "diving or splashing" of the printing plate in the fluid (as the gravity of and/or driving force on the plate surpasses the upwards tension), followed by an uncontrolled "sweeping" out of the printing plate from the developing fluid (see FIGS. 2.1, 2.2 and 2.3).
In trying to achieve this geometrical control, some important supplementary problems make the main problem even much more difficult. One such problem encountered in practice is the secondary difficulty of making a single high quality developing apparatus capable of handling different thicknesses of the support material, and thus covering a wide spread of mechanical strength properties. A further difficulty is the fact that, the silver halide emulsion on the support material is hardened at most only slightly so that the latent image on the printing plate may easily be damaged while coming into contact with any other material or component and that eventual contacting means, as e.g. rollers, can become coated with gelatin and thus contaminating the next printing plates which still have to be processed.
Up to now, a good solution for the above-identified problem has not been. disclosed.